Optical displays, such as backlit liquid crystal displays (“LCDs”), are used in a wide variety of device applications including mobile telephones, personal digital assistants (“PDAs”), electronic games, laptop computers, monitors, and television screens. Optical films are stacked within an optical display in order to enhance brightness and improve display performance without sacrificing battery life. Ideally, optical films are stacked in such a manner that an air gap is maintained between adjacent films to optimize optical performance.
Presently, films used in displays are often provided as individual films to display manufacturers. The films typically include tabs that are useful in orienting and positioning the films, and cover sheets to protect the surfaces of the films. During assembly of a display, the cover sheets of the films are removed, and the films are stacked, one by one, for instance, into a frame that fits between a backlight assembly and an LCD panel. Double-coated rim tape is placed over the stacked films, which seals the edges of the films. A cover sheet is then placed over the rim tape. To finish the display, the cover sheet is removed, and the LCD panel is adhered to the rim tape.
This process is difficult and costly in terms of time and material. Creating tabs on the films increases the amount of waste material that is produced and increases the width of the bezel, or edge, that must extend around the perimeter of the display to cover the tab. Because the tabs extend to the edge of the rim tape, a path is created that allows debris to enter and settle between the films. Removing cover sheets from individual films increases assembly time and the possibility of damaging the films. In addition, as optical films are made in ever thinner variants, it becomes increasingly difficult to handle an individual optical film, by hand or machine. Thus, resolving these problems would increase product output by increasing assembly efficiency and reducing the number of damaged films.
U.S. Pat. No. 7,339,635 (Freking et al.) discloses an approach whereby optical films are stacked and arranged in sub-assemblies to reduce the handling of individual layers in subsequent device manufacturing operations.
The need exists for alternative constructions of, and methods for making, unitary optical film assemblies of prismatic and diffuser films.